If there was a market of people who would pay for such an app, there would be one on the market to satisfy the demand for it. Supply is irrelevant if there is no demand for it in the first place.
Even taking this assertion, it means there is effectively infinite supply so Twitter's service has effectively no monetary value to the consumer. It's still impossible to charge a consumer for it then (and the costs to provide the service have to be paid by a 3rd party in ads).
Edit: It's very difficult to build a network and get to a critical mass like Twitter. I'm still arguing it's demand constrained (people unwilling to pay) because you would see more viable competitors if it were supply.
Even taking this assertion, it means there is effectively infinite supply so Twitter's service has effectively no monetary value to the consumer. It's still impossible to charge a consumer for it then (and the costs to provide the service have to be paid by a 3rd party in ads).
Edit: It's very difficult to build a network and get to a critical mass like Twitter. I'm still arguing it's demand constrained (people unwilling to pay) because you would see more viable competitors if it were supply.